1. Field of the Invention
The present invention relates to methods for processing semiconductor devices. More particularly, the present invention relates to methods for forming isolated semiconductor devices on a single substrate.
2. Background of the Prior Art and Related Information
Integrated circuits having a number of semiconductor devices which are dielectrically isolated but formed on a single substrate are of considerable importance for a number of applications. For example, such devices have increased resistance to radiation damage, since charges induced in the substrate by electron/hole pair creation during radiation events will not affect the dielectrically isolated semiconductor devices. Also, dielectrically isolated devices are very suitable for high voltage applications where high voltages applied to portions of the integrated circuit would otherwise cause breakdown effects to occur in neighboring semiconductor devices. Also, dielectrically isolated semiconductor devices integrated on a substrate can generally tolerate higher operating temperatures than more conventional integrated circuit devices.
A conventional approach to providing dielectrically isolated semiconductor devices has beer to start with a substrate of sapphire and then form individual isolated semiconductor devices on the underlying sapphire substrate. This so-called silicon-on-sapphire approach has proved effective but is quite expensive. As a result, in practice silicon-on-sapphire technology has generally been limited to military applications or other applications where high cost may be justified. Also, the silicon-or-sapphire approach to providing dielectrically isolated semiconductor devices requires processing steps which differ from conventional semiconductor processing techniques making it difficult to readily implement with conventional semiconductor processing equipment.
Various approaches have also been developed which attempt to provide partial or complete dielectric isolation of devices formed on a silicon substrate. Silicon as a substrate has several advantages over the use of sapphire. In particular, silicon is cheaper and, since silicon is employed rather than sapphire, conventional semiconductor processing techniques may be employed to simplify device processing. Various such approaches are illustrated, for example, in U.S. Pat. Nos. 4,507,158; 4,824,795; 4,509,249; 4,554,728; 4,543,706; 4,234,362; 4,771,328; 4,725,562; 4,786,960; 4,819,052; 4,825,277; 4,256,514 and 4,473,598. Nonetheless, the aforementioned approaches have not fully exploited the capabilities of isolated devices on a single silicon substrate in a cost effective and readily implemented process.
Accordingly, a need presently exits for an improved method of processing isolated semiconductor devices on a single semiconductor substrate. Additionally, a need presently exists for providing such an improved method within existing semiconductor processing techniques in a reproducible and cost effective manner.